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Related Experiment Videos

When red lights look yellow.

Joanne M Wood1, David A Atchison, Alex Chaparro

  • 1School of Optometry, Queensland University of Technology, Brisbane, Australia. j.wood@qut.edu.au

Investigative Ophthalmology & Visual Science
|October 27, 2005
PubMed
Summary
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Red train signals may appear yellow to drivers at long distances due to positive defocus, not just progressive-addition lenses. This color misperception poses a significant safety risk, potentially leading to accidents.

Area of Science:

  • Visual perception
  • Ophthalmology
  • Transportation safety

Background:

  • Red signals conventionally indicate danger.
  • Train drivers report red signals appearing yellow at distances around 900m, particularly with progressive-addition lenses.

Purpose of the Study:

  • Investigate the phenomenon of red train signals appearing yellow at long distances.
  • Determine the factors contributing to this color misperception.

Main Methods:

  • Laboratory study with visually normal participants examining defocus, target size, illumination, and surround characteristics.
  • Field study validating laboratory findings by measuring defocus and misperception distances, and assessing time-of-day effects.

Main Results:

Related Experiment Videos

  • Small red targets (1 min arc) appeared yellow with mild positive defocus (+0.75 D) under bright light (1910 cd/m²).
  • Field study confirmed similar defocus levels; time of day influenced misperception, with no issues at night.

    • Conclusions:

    • Color misperception is linked to positive defocus, not exclusively progressive-addition lenses.
    • This visual anomaly presents a critical safety concern, with potential for severe accidents and fatalities.